As the ceramic honeycomb structural body used for carrying a catalyst for the purification (conversion) of the exhaust gas from vehicles is mainly used an integrally structural product made from a low thermal expansive cordierite or the like. Such a ceramic honeycomb structural body is common to support a material having a high specific surface area such as an active alumina or the like, and a catalyst metal such as platinum or the like on its surface. Also, in engines used under excess oxygen conditions such as lean burn engine and diesel engine, NOx occlusion agent made from an alkaline earth metal such as Ba or the like for the NOx treatment is carried on the surface of the structural body.
In order to further improve the purification (conversion) performance of the ceramic honeycomb structural body, it is effective to increase the contact efficiency between the exhaust gas and the noble metal catalyst or the NOx occlusion agent. For this end, it is important to carry the catalyst on the surface of the partition wall of the ceramic honeycomb structural body in a well-dispersed condition. (See JP-A-10-263416)
Also, as the ceramic honeycomb structural body, there is proposed a technique for improving the reactivity by adjusting the pore size distribution (See JP-A-03-68456, JP-A-08-229412, JP-A-2001-187318, JP-A-2001-187320, JP-A-10-43588). The contents of JP-A-10-263416, JP-A-03-68456, JP-A-08-229412, JP-A-2001-187318, JP-A-2001-187320 and JP-A-10-43588 are incorporated herein by reference in their entirety.